The Storm, Dust storm of 2007 Options

[OWW]

Oh no...This is getting bad:

The new and potentially bleak outlook is a stark shift from the prognosis earlier this week.

The dusty squall has reduced direct sunlight to Mars' surface by nearly 99 percent, an unprecedented threat for the solar-powered robotic explorers. If the storm keeps up and thickens with even more dust, officials fear the rovers' batteries may empty and silence the robotic explorers forever.

Opportunity's energy-gathering ability has been slashed to a dangerous 280 watt-hours-enough power to light only three 90-watt light bulbs.

"The worst-case scenario is that enough dust in the sky decreases solar energy to the point that we have to shut down too many things to save power," Lemmon said. "The rovers keep their battery alive by keeping their electronics alive."

"The reality of the situation is that we're limited as to what we can do from the ground by cutting power use," Callas said. "If it continues to worsen and stay that way, it's a survivability issue for Opportunity. If Mars wants to kill the rovers, it can."

http://www.space.com/news/070705_dusty_rovers.html

[hendric]

Is it possible that the Tau reading is just a single point on a line, ie the Tau could be 4.6 now, but could be lower or higher before and after that reading. Tau comes from looking at the sun, right? So power produced could be slightly off from what you expect because the dust isn't consistent either across the sky, or from morning to evening.

[Pertinax]

Is it possible that the Tau reading is just a single point on a line, ie the Tau could be 4.6 now, but could be lower or higher before and after that reading. Tau comes from looking at the sun, right? So power produced could be slightly off from what you expect because the dust isn't consistent either across the sky, or from morning to evening.

I would be strongly suspicious of any answer other than 'absolutely'.

The dust in the atmosphere certainly varies on short time scales -- they do on earth. Also, as you noted the extinction of sunlight would be greater for lower sun angles than higher for any given tau, as the effective optical depth increases with a lower sun (sun having to shine though a greater volume of air & dust). I have wondered myself how for a constant tau the sky appearance (including of course scattered light) would vary.

FWIW: http://marswatch.astro.cornell.edu/Bell_etal_SkyColor_06.pdf

-- Pertinax